1. Field of the Invention
The present invention relates to cathode ray tubes (CRTs) with front panel assemblies having tensed shadow masks supported on the faceplate of the CRT by mask support structures affixed to the faceplate. More specifically, the present invention relates to a front panel assembly with an efficacious mask support structure and a method of making same.
2. Discussion of the Related Art
As is known in the art, there are color CRTs having front panel assemblies comprising thin foil shadow masks welded under tension to mask support structures affixed to the faceplate of the CRT. These shadow masks by definition act as parallax barriers to direct the electron beamlets to the proper phosphor dot on the CRT screen. Exemplary mask support structures for known types of CRT front panel assemblies are illustrated in FIGS. 1 and 2. These structures are more fully disclosed and claimed in U.S. Pat. Nos. 4,737,681 and 4,891,545 respectively, commonly assigned to the Assignee hereof.
The front panel assembly 9 of FIG. 1 comprises a glass faceplate 19 carrying a phosphor screen 12 and a mask support structure 11 which comprises a ceramic body 13 and a metal alloy cap 15, of approximately thirty two mils thick stock, attached to the body 13 by a devitrifying frit 17. The whole mask support structure is then attached to the CRT faceplate 19 with devitrifying frit 17. The metal alloy cap 15 is then ground to provide a weld land 35 at the correct "Q" height. A tensed, thin, foil shadow mask 18 is then welded directly, i.e. without intervening filler metals, to the weld land 35 of the mask support structure.
As seen in FIG. 2, the mask support structure 23 is comprised of an inverted "V" - shaped metal alloy 25, of approximately twenty-four mil thick stock, which is filled with devitrifying frit 17 and secured by additional devitrifying frit to the faceplate 19. The mask support structure 23 is then ground to provide a weld land 35 at the correct "Q" height. The tensed foil mask 18 is then welded to the weld land 35.
While the embodiments of FIGS. 1 and 2 are structurally adequate for forming a tensed mask color CRT front panel assembly, some economies of manufacturing may be had through utilization of the presently disclosed invention.
It is an object of the present invention to provide a front panel assembly for a tensed mask color CRT which is inexpensive and utilizes little metal, while providing a mask support structure capable of accepting welds strong enough to hold the foil mask in tension thereon. It is also preferable that this mask support structure be controllable to close tolerance in the overall height thereof.